The Opiliones tree of life: shedding light on harvestmen relationships through transcriptomics

Abstract

Opiliones are iconic arachnids with a Palaeozoic origin and a diversity that reflects ancient biogeographic patterns dating back at least to the times of Pangea. Owing to interest in harvestman diversity, evolution and biogeography, their relationships have been thoroughly studied using morphology and PCR-based Sanger approaches to infer their systematic relationships. More recently, two studies utilized transcriptomics-based phylogenomics to explore their basal relationships and diversification, but sampling was limiting for understanding deep evolutionary patterns, as they lacked good taxon representation at the family level. Here, we analysed a set of the 14 existing transcriptomes with 40 additional ones generated for this study, representing approximately 80% of the extant familial diversity in Opiliones. Our phylogenetic analyses, including a set of data matrices with different gene occupancy and evolutionary rates, and using a multitude of methods correcting for a diversity of factors affecting phylogenomic data matrices, provide a robust and stable Opiliones tree of life, where most families and higher taxa are precisely placed. Our dating analyses using alternative calibration points, methods and analytical parameters provide well-resolved old divergences, consistent with ancient regionalization in Pangea in some groups, and Pangean vicariance in others. The integration of state-of-the-art molecular techniques and analyses, together with the broadest taxonomic sampling to date presented in a phylogenomic study of harvestmen, provide new insights into harvestmen interrelationships, as well as an overview of the general biogeographic patterns of this ancient arthropod group.

Light from dark: A relictual troglobite reveals a broader ancestral distribution for kimulid harvestmen (Opiliones: Laniatores: Kimulidae) in South America

“…[ 6 , 17 , 34 ]). One remarkable congruence between our phylogram and the Opiliones transcriptomic-based phylogenetic hypothesis of Fernández et al [ 35 ] is the the sister group relation of Assamioidea with the Samooidea+Zalmoxoidea clade (albeit with low support, PP = 0.77). The chronogram failed to recover this relationship, placing Assamiidae as sister to Pyramidopidae, but with no support (PP = 0.2).…”

A new species of Tithaeidae (Arachnida: Opiliones: Laniatores) from Mindanao reveals contemporaneous colonisation of the Philippines by Sunda Shelf opiliofauna

“…A compact 34-taxon dataset was generated, comprising 22 specimens of Tithaeus (encompassing localities in Mindanao, the Thai-Malay Peninsula, the Indo-Chinese plate and Borneo), two Podoctidae, two Petrobunidae, two Assamiidae, two Epedanidae, two Zalmoxidae and two Sandokanidae. The sandokanid outgroups were used to root the tree, following the phylogenomic tree topology of Fernández et al (2017). This dataset is referred to, henceforth, as Dataset 1.…”

“…The genus was later elevated to family level on the basis of molecular phylogenetics and re-examination of genitalic structures (Sharma and Giribet 2011;Sharma et al 2011a), both of which suggested a closer relationship to Podoctidae . Although the sister group of Tithaeidae is not clearly established by molecular phylogenetic studies, in part owing to its absence from phylogenomic datasets (Fernández et al 2017), the increased taxonomic sampling of this lineage and re-analysis of phylogenetic placement corroborated a placement distant from Epedanidae. One outstanding matter not addressed during the establishment of Tithaeidae, owing to previous limitations in taxonomic sampling, was the status of the Bornean species Metatithaeus rubidus.…”

Two new species of Petrobunus from China (Opiliones: Laniatores: Petrobunidae)

“…nov. is the northernmost Laniatores species from China. (Fernández et al 2017). The epedanoids are instead united by a characteristic biogeographic distribution: they are all largely restricted to southeast Asia.…”